Über Algae Eaters: The Lawnmower Blennies (Full Article)

Author: Scott Michael

Photographer: Scott Michael

Known for their algae-eating abilities, blennies of the genus Salarias can make outstanding reef residents provided certain basic requirements are met. The master reefkeeper explains how you can add these blennies to your own setup.

Many of the blennies are algivores, and because of this, they are often introduced to the aquarium to control hair algae. The most popular with aquarists are the lawnmower blennies (especially the jeweled or lawnmower blenny [Salarias fasciatus]). The 13 species in the genus Salarias belong to the subfamily Salariinaeand are often collectively referred to as combtooth blennies. They are not the most colorful members of the family, but the color usually consists of bands, stripes, and spots in hues of brown, green, and cream. Their color patterns typically help them to disappear against the reef substrate.

Biology

The Salarias species are residents of tropical, shallow coastal habitats. They typically are found on fringing reefs or on lagoon patch reefs and rubble patches. These blennies regularly live among coral rubble, macroalgae, or branching stony corals or at the base of sponges. Salarias spp. are most often found at depths of less than 15 meters (50 feet). There is one newly described species (in 2005), S. reticulatus, that inhabits fresh water in south India.

These blennies pound the substrate with their flexible jaws and comb-like teeth. While they do eat some algae (the amount varies from one species to the next), recent studies have shown their primary source of food is detritus in the form of detrital aggregates. Because detritus is often overlooked in food-habit studies, its importance as Salarias food has long been overlooked.

These blennies scrape this material off hard surfaces (e.g., coral rock, dead coral skeletons), along with some algae. They will also incidentally ingest tiny invertebrates. For example, the diet of S. fasciatus has been reported to include filamentous algae, diatoms, foraminiferans (shelled protozoa), tiny crustaceans, detritus, and sand. On occasion, this species will also consume fish eggs, sponges, and small snails. They ingest a significant amount of calcium carbonate as they feed, which is not uncommon for herbivores with less selective feeding tactics. While many of the Salarias spp. eat some algae, some steer away from the filamentous forms that can overgrow our aquariums. For example, S. patzneri selectively feeds on smaller particles less than 125 mm in size (mainly detritus) and avoids those in excess of 250 mm (that is, algal filaments).

These blennies lay demersal eggs, which they deposit in shells (e.g., empty tridacnid valves). The male tends the eggs until they hatch.

The Jeweled Blenny: A Case Study

Salarias spp. spend most of their time in repose on hard substrates. When threatened, they dive into a crack or hole. While data is lacking for most species, at least one species has been studied in depth and is known to be territorial. This species, the jeweled blenny (S. fasciatus), has been studied in great detail on the reefs around Heron Island, Great Barrier Reef. (While it cannot be said emphatically that the behavioral trends in S. fasciatus can be applied to all members of the genus, it is likely that like-sized congeners do behave similarly.)

These researchers found that S. fasciatus takes around 3,000 bites at the substrate per day (that was over twice the number of bites taken by the sympatric Ward’s damsel [Pomacentrus wardi]). This blenny feeds continuously throughout the day, reaching a peak in foraging activity at about 12:00 PM (another study reports a peak in feeding rates at 3:00 PM). Around Heron Island, the feeding rate dropped down at 1:00 PM, then increased again from 2:00 to 4:00 PM. It has been suggested that this dip in feeding rates may be in response to an increase in feeding activity by large herbivores. Parrotfishes, surgeonfishes, and rabbitfishes may invade blenny territories at this time and preclude the blenny from feeding. While the jeweled blenny has a full gut as early as 7:00 AM, the rate of gut evacuation increases thereafter, as does the feeding rate.

Townsend and Tibbetts (2004) looked at interspecific aggression in S. fasciatus. It was found that the jeweled blenny is most aggressive toward other blennies—in particular species/individuals that are the same size or smaller than it is. About 90 percent of the blennies (including conspecifics, Atrosalarias fuscus, and Ecsenius mandibularis) that entered an S. fasciatus territory were chased, while 20 percent of the damsels that invaded its turf were hounded. On rare occasions, they do chase other herbivores, but they typically ignore non-trophic competitors. It was found to be much less aggressive than the sympatric Ward’s damsel.

The jeweled blenny (as well as some other species) coexists in damselfish territories, with the two species typically ignoring one another. On Heron Island reefs, S. fasciatus is often found living within the territory of P. wardi. Even though you might think that they are food competitors, this relationship may be beneficial to both fishes.

There may be several reasons the damsel tolerates the blenny’s presence. By chasing out confamilials of similar or smaller size, S. fasciatus saves the damsel energy and time. In this way, the Salarias may exclude smaller blennies with higher metabolic needs from the damsel’s territory (reducing competition). It may also be that the damsels and blennies do not have as much dietary overlap as once thought. The territorial pomacentrids are selective grazers, while the salariine blennies are less discriminating. The damsels are able to get enough to eat in a shorter time period than the blenny. The pomacentrid can then invest less time in feeding and more time in territory defense.

Captive Care

Of the 13 species in the genus, one is common in the aquarium trade and several others make regular appearances in local fish stores. As mentioned above, the members of the genus Salarias are often employed to aid in the control of filamentous algae. In fact, S. fasciatus is one of the most popular algae-eating fishes. They are also fascinating to watch. They will dash from one location to the next and then pound at the substrate with their open jaws (they look like an aquatic woodpecker!). When threatened, they will dart into a crevice or back into a hole in the rock, often leaving their head protruding so that they can see what is going on around them.

Feeding Habits

Individuals vary in their usefulness in controlling some of the dreaded hair algae species. Some of the larger species (e.g., S. fasciatus) regularly consume filamentous algae. However, there are individual Salarias that tend to ignore it, choosing instead to rasp diatoms and other unicellular microalgae off the aquarium glass or live rock. It has been suggested that if you frequently feed them other foods, they will be more reluctant to dine on the dreaded hair algae.

Make sure your lawnmower blennies are getting enough to eat by regularly examining the contour of their bellies and dorsal musculature. If they are looking pinched in, you need to feed them more or move them to a tank with a better microalgae crop. An occasional specimen may also browse on macroalgae, although they are not as well adapted to eating these plant types. Another benefit to keeping these fishes in the home aquarium is that their feeding activity will stir up sediment on rock, putting detritus in suspension where it can be removed by mechanical filters (larger individuals are especially good at stirring up detritus).

There is no doubt that the Salarias spp. tend to do better when there is a healthy film of microalgae in the tank. For this reason, they are best introduced to a tank that has been set up for several months. This will ensure there is enough food available for them if they initially refuse added aquarium fare. With time, many individuals will accept frozen preparations for herbivores and more meaty foods (e.g., brine shrimp, mysid shrimp). Some prefer pelletized foods, which they pluck from the aquarium bottom. (Be aware: there is much individual variation in what these fishes will eat—one S. fasciatus may consume anything you put in the tank, while another may ignore any introduced food.)

If your tank has plenty of algae, then you can get away with feeding lawnmower blennies several times a week. In the wild, they continually rasp at hard substrate throughout the day. Therefore, if algae is in short supply in your tank, you may have to add food several times a day. If they refuse introduced foods, you will need to have a large enough tank and a healthy enough algal crop to sustain them. This means a tank that is at least 55 gallons or more for one of the larger members of the genus.

When you consider that this fish may take over 3,000 bites a day, removing an average of 2.19 milligrams of dry-weight epilithic (growing on rocks) algae, it should not be surprising that they can quickly decimate a crop of filamentous algae. For example, I have seen a couple of S. fasciatus decimate a large filamentous algae crop from a moderate-sized tank in a matter of weeks. The reef aquarist with an algal plague may be encouraged by this fact, but it can spell doom for your Salarias if it refuses to accept other foods. Unfortunately, there is no guarantee that your salariine blenny will eat other foods, but as indicated above, many will.

Tankmates

The best rule of thumb is to keep only one Salarias sp. per tank. They will definitely fight with members of their own kind and with other species in the genus. If your tank is larger, you can house a pair of conspecifics. You may even get away with keeping several congeners in the same tank if the aquarium is very large (e.g., 180 gallons or more). While disputes may occur along territory boundaries in a larger aquarium, if there is enough space, they can and will avoid one another and these disputes will not become deadly. To the best of my knowledge, there are no known sexual dimorphisms or differences in colors between the sexes, so selecting a heterosexual pair is more a matter of luck than skill. It may be that males get larger than females, but more research is needed to confirm this.

Salarias spp. occasionally attack other fish species. For example, I have had them bite seahorses and pipefishes. I have also had them bite the bodies and fins of herbivores (e.g., tangs, rabbitfishes) and omnivores (e.g., trunkfishes). You might not actually see a lawnmower blenny nipping at its tankmates, but you may see telltale signs of its attacks—when they nip an adversary, they often leave marks on the body and fins. Their assaults may also result in torn fins. The lawnmower blennies will pick on other blennies. If they are in the tank first and/or are larger than a blenny tankmate, they will typically chase and nip it until the other blenny leaps from the tank, hides incessantly in the reef, or hangs in the aquarium corners. Smaller blennies (e.g., Ecsenius spp.) are especially vulnerable to Salarias attack. If the tank is large enough, and if the blenny is well fed, it is not uncommon for the Salarias spp. to ignore fish tankmates that are not related or similar in shape and behavior (the latter would include elongated bottom-dwellers, like clinid blennies, tube blennies, triplefins, and some gobies).

Salarias spp. are usually not dangerous to corals or tridacnid clams, but an occasional individual may nip at these ornamental invertebrates (they are less likely to exhibit this behavior than some of the other blennioids). When feeding, they may knock snails off the aquarium glass onto their backs, exposing them to attack by crustaceans and malacophagous (snail-eating) fishes. Certain larger Salarias spp. have also been known to attack and eat more gracile shrimps (e.g., anemone shrimps) and to nip the tips off serpent star arms, but these are rare events that should not dissuade the reefkeeper from employing them to help control hair algae. The blennies have been known to bail out of an open aquarium. Therefore, you will need to employ some type of cover to keep them in the tank. They will also leap into overflow boxes.

That ends our examination of the salariine blennies. Not only are these fishes interesting residents in the aquarium, but they are also great utility fishes that earn their keep! They are voracious herbivores that can help decimate and control pestilent flora in the home aquarium.